The long range objective of our research is to develop an understanding of the physiological and psychological aspects of pain perception in order that we may provide improved treatment for patients with chronic pain. Pursuant to this goal, we propose in this grant to continue neurophysiological studies of primary afferent nociceptive units. It will be our objective to: 1) determine the peripheral neural coding mechanism for thermal and mechanical pain perception, 2) determine the peripheral neural mechanism for hyperalgesia induced either from cutaneous injury or peripheral nerve injury, and 3) determine the effects of therapeutic modalities, such as electrical stimulation of the peripheral nerve, on the activity and responses of primary afferent nociceptive units. We will also conduct psychophysical studies of pain perception in patients with chronic pain and in normal human subjects. The objectives of this work are to: 1) obtain a better understanding of how different patients perceive pain with the goal of quantifying the amount of pain from which a particular patient suffers, and 2) obtain a measure of how therapeutic interventions, such as peripheral nerve stimulation, affect pain perception.